A New Co-free Ni-Based Alloy for Gas Turbine and Exhaust Valve Applications

Abstract

A new Ni-based cast-and-wrought alloy designed for high temperature strength, stability, notch ductility, and minimal elevated temperature dwell fatigue crack growth rate has been laboratory developed and scaled up in the mill. Based on studies of a relatively wide compositional space, a Co-free composition was selected. Other properties, including tensile strength, stress rupture, creep, low cycle fatigue, oxidation, and sulfidation resistance, as well as hot workability were also studied. Several heat treatments were developed to achieve property balances as appropriate for various end-user applications such as those limited by damage tolerance, creep, fatigue, or tensile strength. Microstructural stability after extended exposure at temperatures ranging from 704 to 871 °C was studied. Multiple 12-ton heats have been successfully processed as VIM/VAR and VIM/ESR ingots converted into forged billets, rolled bar, and strip products. Potential applications for this alloy include turbine disks, gas turbine engine casings, high temperature fasteners, heavy duty diesel engine exhaust valves, and high temperature gaskets. This paper discusses alloy and process development as well as microstructure--property relationships of the alloy.